In the usual fluorescent discharge lamp starting circuitry it is a common practice to employ an inductive type ballast and a glow lamp type starter with the lamp reignition voltage considerably lower or less than the ionization voltage of the glow lamp. Generally, the fluorescent lamp is activated by the ballasted line voltage and the resultant operational lamp voltage is of a value much less than the voltage necessary to ionize the glow lamp. Thus, the glow lamp is not reignited which would, in turn, undesirably short-circuit and turn off the fluorescent lamp.
Also, there are some fluorescent lamp operating systems which are less expensive than the above-mentined inductive ballast systems or at least could be designed to be more economical than the ordinary inductive ballast system. Specifically, fluorescent lamp starting systems employing a resistor-type ballast have an economic advantage over the ordinary inductor apparatus. Since resistors are less expensive than inductors. An inductor of reduced size which is not required to conduct the full lamp current is another example of enhanced circuitry for operating fluorescent lamps.
Unfortunately, it has been found that ballast circuitry utilizing a ballast resistor tends to produce a lamp voltage having a relatively high peak portion as compared to the ionization voltage of a glow starter. Because the AC line voltage falls below the lamp operating voltage, reverses and builds up in the opposite polarity to the lamp operating voltage, the lamp is not operational for an extended period of time and a substantial decay in ionization wihin the lamp takes place during this non-operational period. Accordingly, a relatively large voltage is required to reignite the lamp and this relatively larger voltage exceeds the ionization voltage of a glow starter. Thus, the glow starter would be activated each cycle which, in turn, would undesirably short-circuit and causes a turn off of the fluorescent lamp. This effect can be countered by reducing lamp length and hence wattage which is generally proportional to length, however, the result is a low wattage lamp of poor efficiency.
In another aspect, a non-linear dielectric element may be utilized to develop a pulse voltage for igniting a fluorescent lamp whereupon a reduction in lamp length or wattage is not required. However, non-linear dielectric elements are characterized by the capability of accepting a charge up to a given value and to then suddenly cease accepting a charge. Thereupon, a very large pulse voltage is developed due to the abrupt discontinuance of current flow in the usual or normal inductive ballast. Accordingly, a lamp voltage is developed which tends to have a peak value much higher than the ionization voltage of a glow starter if one is employed. Thus, the peak lamp voltage reignites the glow starter which, in turn, short-circuits the fluorescent lamp and undesirably discontinues operation of the fluorescent lamp.
One known attempt to remedy the above-mentioned undesirable conditions included a system having a thermal relay heater connecting a ballast to the lamps with the relay contacts coupled to a glow starter shunting the lamp. Although the above-described heater-switch combinations have been and still are widely used in numerous applications, it has been found that the extended period required to cool the heater before resetting of the thermal relay can be effected is most undesirable and severly restrictive of the desired operational capabilities.